Search

We consider the Search for ExtraTerrestrial Intelligence (SETI) activities from a bioethical standpoint. In particular, we argue that there is a moral duty to search for other intelligent beings in the Universe. Some of them could – and are likely to be – morally enhanced in the sense that they are not only capable of unmistakable moral reasoning but are also capable of consistently acting upon the results of such deliberations. Even if the probability of finding such morally superior beings is small, it is higher than zero in any case; in fact, our astrobiological knowledge suggests that this probability is significant. Hence, there are both deductive and inductive arguments for the proposition that our duty is to search for such morally superior extraterrestrial beings. In other words, there is a duty to undertake and support our SETI efforts. The argument to that effect runs parallel to some of the arguments deployed in current debates on human moral enhancement.

Now that we know that Earth-like planets are ubiquitous in the universe, as well as that most of them are much older than the Earth, it is justified to ask to what extent evolutionary outcomes on other such planets are similar, or indeed commensurable, to the outcomes we perceive around us. In order to assess the degree of specialty or mediocrity of our trajectory of biospheric evolution, we need to take into account recent advances in theoretical astrobiology, in particular (i) establishing the history of habitable planets' formation in the Galaxy, and (ii) understanding the crucial importance of "Gaian" feedback loops and temporal windows for the interaction of early life with its physical environment. Hereby we consider an alternative macroevolutionary pathway that may result in tight functional integration of all sub-planetary ecosystems, eventually giving rise to a true superorganism at the biospheric level. The blueprint for a possible outcome of this scenario has been masterfully provided by the great Polish novelist Stanis{\l}aw Lem in his 1961 novel Solaris. In fact, Solaris offers such a persuasive and powerful case for an "extremely strong" Gaia hypothesis that it is, arguably, high time to investigate it in a discursive astrobiological and philosophical context. In addition to novel predictions in the domain of potentially detectable biosignatures, some additional cognitive and heuristic benefits of studying such extreme cases of functional integration are briefly discussed., Comment: 20 pages, 1 figure; accepted in "Origins of Life and Evolution of Biospheres"

Recent years have seen both a revival of space programs, mostly propelled by private industry's increasing interest, but also the emergence of strong resistance to human space activities on several levels. This is partly a manifestation of a wider counter-Enlightenment Zeitgeist, as detectable in other sectors of public life in the West, and partly a reaction against the widespread engagement of the private sector. While it still does not dominate the discourse on space issues, space skepticism is surprisingly wide-ranging and decentralized phenomenon, gathering together heterogeneous strands of thought from pro-Enlightenment liberals to rabid "deep ecology" activists to philosophical pessimists to antiglobalists of all colors. There has been precious little in way of actively opposing this cultural trend so far, however. While space engineers and entrepreneurs conduct their "business as usual", there are plethora of risks hidden in this cultural climate, esp. if one adopts much repeated (and rarely adequately understood) maxim that "politics is downstream of culture." The present article will review major strands of thought within this big tent cultural movement, offer plausible counter-arguments to space skeptics, and outline important cultural and public-outreach work which needs to be done to balance the scales., 16 pages, no figures; accepted for publication in "Futures"

Standard reductionist narrative about the necessity of complex systems arising from simple subsystems can be undermined from multiple directions. Here, I shall suggest an unexpected way of such undermining which occurs upon joining our best understanding of the future evolution of the universe (as outlined by physical eschatology) with the continuity thesis which plays the key role in studies of the origin of life (abiogenesis). Many aspects of evolution - including physical, chemical, and astrobiological evolution - would look quite different from what we empirically find around us at the present epoch if the history of the universe within our cosmological horizon were to be observed from a timeless ?Archimedean? point. Avoiding the pitfalls of this chronocentric bias leads to several unexpected conclusions, one of them being that the directed panspermia, coupled with advanced biotechnology, represents the most probable origin of almost all phylogenetic lineages in the universe. Therefore, complex lifeforms are required for emergence of (almost) all simple lifeforms. This has several counterintuitive and unexpected philosophical consequences.

Observational data suggest that a belt of planetesimals is expected close to the snow line in protoplanetary disks. Assuming there is such a belt in TRAPPIST-1 system, we examine possibilities of water delivery to the planets via planetesimals from the belt. The study is accomplished by numerical simulations of dynamical evolution of a hypothetical planetesimal belt. Our results show that the inner part of the belt is dynamically unstable and planetesimals located in this region are quickly scattered away, with many of them entering the region around the planets. The main dynamical mechanism responsible for the instability are close encounters with the outermost planet Trappist-1h. A low-order mean-motion resonance 2:3 with Trappist-1h, located in the same region, also contributes to the objects transport. In our nominal model, the planets have received non-negligible amount of water, with the smallest amount of $15$\% of the current Earth's water amount (EWA) being delivered to the planet 1b, while the planets Trappist-1e and Trappist-1g have received more than $60$\% of the EWA. We have found that while the estimated efficiency of water transport to the planets is robust, the amount of water delivered to each planet may vary significantly depending on the initial masses and orbits of the planets. The estimated dynamical "half-lives" have shown that the impactors' source region should be emptied in less then 1~Myr. Therefore, the obtained results suggest that transport of planetesimals through the system preferably occurs during an early phase of the planetary system evolution., Comment: 12 pages, 8 figures; MNRAS, accepted for publication

There have been tantalizing indications from many quarters of physical cosmology that we are living in the multiverse - a huge set of cosmological domains ("universes"). What is the structure of this larger whole is an entirely open problem on the interface between physics and metaphysics. A goal of the present paper is to draw attention to the connection between this problem and an old and celebrated puzzle in mathematical physics. Among the unresolved problems David Hilbert posed in 1900 as a challenge for the dawning century, none is more philosophically controversial than the Sixth Problem, requiring the axiomatization of physical theories. In the new century and the new millennium, this problem has remained a challenge, usually swept under the rug as "not belonging to mathematics" (as if that impacts its epistemical status) or simply "unresolved". Recent radical ontological/cosmological hypothesis of Max Tegmark, identifying mathematical and physical structures, might shed some new light onto this allegedly antiquated subject: it might be the case that the problem has already been solved, insofar we have formalized mathematical structures! While this can be seen as "cutting the Gordian knot" rather than patiently resolving the issue, we suggest that there are several advantages to taking Tegmark's solution seriously, notably in the domain of (future) physics of the observer. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. ON176021: Visible and Invisible Matter in Nearby Galaxies: Theory and Observations and Grant no. ON179048: The Theory and Practice of Science in Society: Multidisciplinary, Educational, and Intergenerational Perspectives]

The problem of the extent of habitable zones in different kinds of galaxies is one of the outstanding challenges for contemporary astrobiology. In the present study, we investigate habitability in a large sample of simulated galaxies from the Illustris Project in order to at least roughly quantify the hospitality to life of different galactic types. The pioneering study of Dayal et al. (2015) is critically examined and some of its results are amended. In particular, we find a tentative evidence for a second mode of galactic habitability comprising metal-rich dwarfs similar to IC 225, LMC or M32. The role of the galactic environment and the observation selection effects is briefly discussed and prospects for further research on the topic outlined., Comment: 27 pages, 8 figures, to appear in MNRAS

Recent discussion of the alleged adverse consequences of space colonization by Phil Torres in this journal is critically assessed. While the concern for suffering risks (s-risks) should be part of any strategic discussion of the cosmic future of humanity, the Hobbesian picture painted by Torres is largely flawed and unpersuasive. Instead, there is a very real risk that the skeptical arguments will be taken too seriously and future human flourishing in space delayed or prevented.

It is well-known that the chances of success of SETI depend on the longevity of technological civilizations or, more broadly, on the duration of the signs of their existence, or technosignatures. Here, we re-examine this general tenet in more detail, and we show that its broader implications were not given the proper significance. In particular, an often overlooked aspect is that the duration of a technosignature is in principle almost entirely separable from the age of the civilization that produces it. We propose a classification scheme of technosignatures based on their duration and, using Monte Carlo simulations, we show that, given an initial generic distribution of Galactic technosignatures, only the ones with the longest duration are likely to be detected. This tells us, among other things, that looking for a large number of short-lived technosignatures is a weaker observational strategy than focusing the search on a few long-lived ones. It also suggests to abandon any anthropocentric bias in approaching the question of extraterrestrial intelligence. We finally give some ideas of possible pathways that can lead to the establishment of long-lived technosignatures., Comment: Accepted for publication in The Astronomical Journal

The opera of Stanislaw Lem present us with a kaleidoscope of ideas and concepts all linked, in one way or another, to one key issue: the place of evolving minds in the evolving universe. In particular, the idea of fragmented, non-conscious intelligences belonging to neither strictly natural, nor strictly artificial, realms has been presented throughout his writing career; we shall analyse how these ideas are implemented in an early (The Invincible), as well as a late (Peace on Earth) novel, which superficially have very little in common. A case will be made that this idea can fruitfully connect with several recent developments in astrobiology, evolutionary biology, and philosophy of mind. As in so many other things, Lem has been decades ahead of his time, as contemporary pop-cultural elaborations clearly demonstrate.

An often used assumption in astrobiology and SETI studies is that the average condition of the present universe is typical in time, and that many of the relevant physical quantities can be treated as stationary. The uncritical adoption of such assumption of ‘temporal Copernicanism’ can lead to wrong conclusions, and should be treated with extreme care, if not discarded altogether.

Both human bioenhancement and human activities in space are two great projects of our species for this millennium. Both are often motivated by exalted and noble purposes, the most important being the avoidance of the “ultimate harm” or a similar extremely undesirable outcome. Both projects are often met with fierce and even fanatical opposition. Motivations for opposition are heterogeneous—at least when surveyed superficially. This chapter puts forward the hypothesis that the ultimate source of this often-hysterical opposition is anthropocentrism: the tendency to separate humans, as they are today, from their natural and evolutionary embedding and assign high essential value to their current make-up. There is a strong anthropocentric cartel with vested interest in human exceptionalism, geocentrism, and other forms of parochial, self-indulgent, small-scale, and solipsist thinking. The cartel is the main source of resistance and opposition to both human bioenhancement and colonization of the universe. The anthropocentric stance against colonization of the universe is incoherent and implies magical, rather than scientific, way of thinking. The argument for delayed human exploration and colonization of the universe is, like any other delay-type argument, just a cop-out for avoiding responsibility which resolves nothing of substance.

A methodological problem is inherent in any discussion of extraterrestrial engineering and its detectability: how to distinguish detection signatures of such astroengineering from “natural”, non-intentional, albeit exotic, processes? In practice, searches for traces and manifestations of advanced technological civilizations have been reduced so far to searching for outliers in the allegedly well-known regularities expected from natural astrophysical sources. This procedure, however, is an epistemological minefield, for at least two reasons: (i) prior datasets on which the regularities are based might be contaminated by artefacts, and (ii) the procedure of computation of unobservable quantities usually contains the implicit assumption of the non-intentional nature of sources. In other words, we are facing a Catch-22-type problem: in order to prove the artificial nature of a source, we seemingly need to first assume that it is not artificial. In contrast to most problems in science, this one could possibly be aggravated, rather than reduced, with the progress of our scientific understanding. Some possible recourses, as well as directions for further work toward building a comprehensive methodology of the Dysonian SETI, are discussed.

It has already become a commonplace to discuss postbiological evolution in various contexts of futures studies, bioethics, cognitive sciences, philosophical anthropology, or even economics and SETI studies. The assumption is that technological/cultural evolution will soon entirely substitute for the biological processes which underlie human existence – and, by analogy, the existence of other independently evolved intelligent beings, if any. Various modes of postbiological evolution of humans have been envisioned in both fictional and discursive contexts (uploading, cyborgization, technological singularity, etc.). Little thought has been devoted so far to the question whether these postbiological modes are truly final in both logical and conceptual terms. What lies beyond the postbiological realm? Clearly, only a few radical speculations on the topic can be offered. In this paper, it is argued that in a sufficiently broad subset of scenarios for postbiological evolution there will be a kind of reverse trend: the one of reintegration with the (astro)biological universe, by that point understood in a much wider and more inclusive sense. The argument for such reintegration could be understood through the metaphor of expanding Klein bottle as a symbolic image of the post-postbiological evolutionary trajectories. This kind of trajectory will lead to the state in which products of culture are indistinguishable from the natural environment, suggesting practical consequences for our SETI efforts.

Jared Diamond's argument against extraterrestrial intelligence from evolutionary contingency is subjected to critical scrutiny. As with the earlier arguments of George Gaylord Simpson, it contains critical loopholes that lead to its unraveling. From the point of view of the contemporary debates about biological evolution, perhaps the most contentious aspect of such arguments is their atemporal and gradualist usage of the space of all possible biological forms (morphospace). Such usage enables the translation of the adaptive value of a trait into the probability of its evolving. This procedure, it is argued, is dangerously misleading. Contra Diamond, there are reasons to believe that convergence not only plays an important role in the history of life, but also profoundly improves the prospects for search for extraterrestrial intelligence success. Some further considerations about the role of observation selection effects and our scaling of complexity in the great debate about contingency and convergence are given. Taken together, these considerations militate against the pessimism of Diamond's conclusion, and suggest that the search for traces and manifestations of extraterrestrial intelligences is far from forlorn. Key Words: Astrobiology-Evolution-Contingency-Convergence-Complex life-SETI-Major evolutionary transitions-Selection effects-Jared Diamond. Astrobiology 18, 491-502.

Recent paper by Robert Klee in this journal argues that we should endorse a form of cosmic pessimism due to the inevitable destruction of Earth and humanity, allegedly meaning the complete and total annihilation of all traces of humanity's existence (‘human expunction’). It could be shown that both the physical basis and philosophical methodology used by Klee to reach those bleak conclusions are at best premature and at worst unwarranted and misleading. Even worse, they reflect a mindset of unjustified and narrow-minded technological and societal pessimism, which contributes to the erosion of the Enlightenment values, the loss of public interest in space research and colonization, and could indeed increase vulnerability to real – as opposed to uncertain eschatological – global risks humanity is facing in this millennium.

In a recent paper in this journal, Lingam and Loeb (2018) develop an excellent heuristic for searches for biosignatures vs. technosignatures. We consider two ways in which their approach could be extended and sharpened, with focus on durability of technosignatures. We also note an important consequence of the adopted heuristic which offers strong support to the ideas of the Dysonian SETI., Accepted for publication in Astrobiology

Future human space missions to Mars and beyond may be realized for different research, economic, political or survival reasons. Since space remains a hazardous environment for humans, space exploration and exploitation requires the development and deployment of effective countermeasures. In this paper, we discuss prospects for human enhancement by gene editing, synthetic biology, or implants, for the purposes of future space missions. We argue that there are good reasons to consider such options, and that ethical arguments can be made in favor of human enhancement to enable long-term space exploration.

Both “optimists” and “sceptics” in regard to extraterrestrial intelligence tend to hold the view that we are entitled to an epistemically clear position: either there will be a signal, in the sufficiently general sense, proving the existence of extraterrestrial intelligence (ETI), or no such signal is forthcoming. The distinction, I wish to argue here, is not at all so clear-cut. On the contrary, there are arguments, intrinsic to the subject matter, to the effect that the detection of ETI will be a protracted affair characterized by uncertainty at every step. Such view of SETI discovery mandates different policies from those conventionally discussed in the literature. We should not gear our expectations and publicly promote the view that the Contact will be a clear-cut, Archimedean “Eureka!”-style discovery. In contrast, the tempo and mode of the process of discovery might significantly influence societal and political reactions to the discovery. We should be prepared for such a protracted unfolding of events.

In this article we suggest that the new multidisciplinary field of astrobiology, as a set of the most general research programs dealing with life in its cosmic context is not only useful, but indeed necessary for the full epistemological and methodological justification of the theory of biological evolution. For this purpose, we use three examples of major problems in the philosophy of biology, namely the question of the universality of evolutionary mechanisms, the problem of the origin of the biological hierarchy and the evolvability of evolution problem, which are difficult to address without significant influence of Astrobiology results. We will also consider some of the consequences this has concerning the very philosophy of biology, traditionally understood.

Galaxies represent the main form of organization of matter in our universe. Therefore, they are of obvious interest for the new multidisciplinary field of astrobiology. In particular, to study habitability of galaxies represents one of the main emerging challenges of theoretical and numerical astrobiology. Its theoretical underpinnings are, however, often confused and vague. Here we present a systematic attempt to list and categorize major causal factors playing a role in emergent habitability of galaxies. Furthermore, we argue that the methodology of cosmological merger trees is particularly useful in delineating what are systematic and lawful astrobiological properties of galaxies at present epoch vs. those which are product of historical contingency and, in particular, interaction with wider extragalactic environment. Employing merger trees extracted from cosmological N-body simulations as a new and promising research method for astrobiology has been pioneered by Stanway et al. (2018). We analyse the general issue of applicability of merger trees and present preliminary results on a set of trees extracted from the Illustris Project. In a sense, this approach is directly complementary to using large-scale cosmological simulations to study habitable zones of individual galaxies with high mass/spatial resolution; taken together, they usher a new era of synergy and synthesis between cosmology and astrobiology., 18 pages, 5 figures

The period (roughly) 1990-today is characterized by a big watershed and branching of cosmology into multiple and hitherto unexpected directions. On one side, the generic chaotic/eternal inflation has provided physical grounds for rather wild speculative ideas about the multiverse: the possibly infinite set of cosmological domains (‘universes’). In order to determine how observed features of our universe are (im)probable in the multiverse context requires application of anthropic reasoning which is still controversial in many circles. On the other side, we encounter applications of other speculative physical theories, like the string/M-theory to cosmology, resulting in unusual hypotheses like those of the pre-Big Bang cosmologies. In this period we have also witnessed the birth of physical eschatology as the true ‘cosmology of the future’. This chapter will attempt a survey of these and related developments, with necessary qualifications which accompany any ongoing, evolving research activity.

The alleged improbability of particular critical steps has for quite a long time been one of the favoured arguments of the opponents of universal, cosmic evolution. In a nutshell, the argument goes like this: various realms in which we perceive evolutionary processes are separate domains (implicitly endowed with separate conceptual ‘essences’), since the transition, probabilities between these domains are astronomically small numbers, of the order of 10−100 or smaller. For instance, we should discuss chemical and biological evolution separately, since the probability of spontaneous transition between these two domains – the origin of life or abiogenesis – is extremely small; we are dealing with, in Monod’s famous words, ‘a lucky accident’. Analogous arguments are made for transition between simple microscopic life and complex metazoans, or for transition between conventional animals and intelligent beings with language and culture. These arguments are often behind either creationist or ‘rare-Earth’ argument for uniqueness of our astronomical habitat, as well as behind the scepticism towards astrobiology and SETI studies. The probabilities cited are usually inductive inferences from the prima facie requirements deemed historically necessary in the unique terrestrial case. In the last couple of decades, however, we have obtained much better insight into the dynamical processes underlying some of these requirements – and original ideas emerged as to how we could bypass at least some of them. In that light, it is interesting to consider whether this sea change influenced the sceptical discourse; as I will show, there are reasons to conclude that this kind of scepticism is motivated by extrascientific concerns.

Context. Astrobiological evolution of the Milky Way (or the shape of its "astrobiological landscape") has emerged as one of the key research topics in recent years. In order to build precise, quantitative models of the Galactic habitability, we need to account for two opposing tendencies of life and intelligence in the most general context: the tendency to spread to all available ecological niches (conventionally dubbed "colonization") and the tendency to succumb to various types of existential catastrophes ("catastrophism"). These evolutionary tendencies have become objects of study in fields such as ecology, macroevolution, risk analysis, and futures studies, while a serious astrobiological treatment has been lacking so far. Aims. Our aim is to numerically investigate the dynamics of opposed processes of expansion (panspermia, colonization) and extinction (catastrophic mechanisms) of life in the Galaxy. Methods. We employ a new type of numerical simulation based on 1D probabilistic cellular automaton with very high temporal resolution, in order to study astrobiological dynamics. Results. While the largest part of the examined parameter space shows very low habitability values, as expected, the remaining part has some observationally appealing features that imply, among other things, a reduction in the amount of fine-tuning necessary for resolving the Fermi paradox. Conclusions. Advanced aspects of Galactic habitability are amenable to precision studies using massive parallel computer simulations. There are regions of parameter space corresponding to a quasi-stationary state satisfying observable constraints and possessing viable SETI targets., Comment: Language corrected version, to appear in Astronomy & astrophysics

We outline an argument favoring voluntary moral bioenhancement as a response to existential risks humanity exposes itself to. We consider this type of enhancement a solution to the antithesis between the extinction of humanity and the imperative of humanity to survive at any cost (e.g., by adopting illiberal strategies). By opting for voluntary moral bioenhancement, we refrain from advocating illiberal or even totalitarian strategies that would allegedly help humanity preserve itself. We argue that such strategies, by encroaching upon the freedom of individuals, already inflict a degree of existential harm on human beings. We also give some pointers as to the desirable direction for morally enhanced post-personhood.

We present an isolated Milky Way-like simulation in GADGET2 N-body SPH code. The Galactic disk star formation rate (SFR) surface densities and stellar mass indicative of Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life friendly environments. SFR and stellar component density are calculated averaging the GADGET2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from $10$ to $15$ kpc cylindrical galactocentric distance in $10$ Gyr simulated time span. At $10$ Gyr the simulation results imply the following. Stellar particles which have spent almost all of their life time in habitable friendly conditions reside typically at $\sim16$ kpc from Galactic centre and are $\sim 3$ Gyr old. Stellar particles that have spent $\ge 90 \%$ of their $4-5$ Gyr long life time in habitable friendly conditions, are also predominantly found in the outskirts of the Galactic disk. Less then $1 \%$ of these particles can be found at a typical Solar system galactocentric distance of $8-10$ kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disk around stellar hosts younger than the Sun., Published in MNRAS, no changes, metadata update

We historically trace various non-conventional explanations for the origin of the cosmic microwave background and discuss their merit, while analyzing the dynamics of their rejection, as well as the relevant physical and methodological reasons for it. It turns out that there have been many such unorthodox interpretations; not only those developed in the context of theories rejecting the relativistic ("Big Bang") paradigm entirely (e.g., by Alfven, Hoyle and Narlikar) but also those coming from the camp of original thinkers firmly entrenched in the relativistic milieu (e.g., by Rees, Ellis, Rowan-Robinson, Layzer and Hively). In fact, the orthodox interpretation has only incrementally won out against the alternatives over the course of the three decades of its multi-stage development. While on the whole, none of the alternatives to the hot Big Bang scenario is persuasive today, we discuss the epistemic ramifications of establishing orthodoxy and eliminating alternatives in science, an issue recently discussed by philosophers and historians of science for other areas of physics. Finally, we single out some plausible and possibly fruitful ideas offered by the alternatives., Comment: 53 pages, accepted in "The Studies in History and Philosophy of Modern Physics"

Metaphysics, future studies, and artificial intelligence (AI) are usually regarded as rather distant, non-intersecting fields. There are, however, interesting points of contact which might highlight some potentially risky aspects of advanced computing technologies. While the original simulation argument of Nick Bostrom was formulated without reference to the enabling AI technologies and accompanying existential risks, I argue that there is an important generic link between the two, whose net effect under a range of plausible scenarios is to reduce the likelihood of our living in a simulation. This has several consequences for risk analysis and risk management, the most important being putting greater priority on confronting “traditional” existential risks, such as those following from the misuse of biotechnology, nuclear winter or supervolcanism. In addition, the present argument demonstrates how – rather counterintuitively – seemingly speculative ontological speculations could, in principle, influence practical decisions on risk mitigation policies.

The well-known argument against the Search for ExtraTerrestrial Intelligence (SETI) due to George Gaylord Simpson is re-analyzed almost half a century later, in the light of our improved understanding of preconditions for the emergence of life and intelligence brought about by the ongoing “astrobiological revolution”. Simpson’s argument has been enormously influential, in particular in biological circles, and it arguably fueled the most serious opposition to SETI programmes and their funding. I argue that both proponents and opponents of Simpson’s argument have occasionally mispresented its core content. Proponents often oversimplify it as just another consequence of biological contingency, thus leaving their position open to general arguments limiting the scope of contingency in evolution (such as the recent argument of Geerat Vermeij based on selection effects in the fossil record). They also tend to neglect that the argument has been presented as essentially atemporal, while referring to entities and processes that are likely to change over time; this has become even less justifiable as our astrobiological knowledge increased in recent years. Opponents have failed to see that the weaknesses in Simpson’s position could be removed by restructuring of the argument; I suggest one way of such restructuring, envisioned long ago in the fictional context by Stanislaw Lem. While no firm consensus has emerged on the validity of Simpson’s argument so far, I suggest that, contrary to the original motivation, today it is less an anti-SETI argument, and more an astrobiological research programme. In this research programme, SETI could be generalized into a platform for testing some of the deepest assumptions about evolutionary continuity and the relative role of contingency versus convergence on unprecedented spatial and temporal scales.

Search for ExtraTerrestrial Intelligence (SETI) is now more than half a century old and has provoked enough discussion on technical, philosophical, and popular level, much of it critical. Historically, the criticism of SETI has been strong enough to heavily influence the course of research, so that there is a significant interest in discerning the nuances and fine points of critical argumentation. In this paper, I outline the two major forms of SETI scepticism, “fundamentalist” and “instrumentalist,” which are often conflated in the published literature, both technical and popular. Precise delineation between these two types of scepticism is important for future research as a part of a wider taxonomic project, the build-up of SETI theory, as well as for smooth joining of SETI with the ongoing astrobiological revolution. Resolving the confusion in this respect is likely to lead to an improved atmosphere and heightened public image of future SETI searches and related activities.

I reconsider a type of counterfactual argument often used in historical sciences on a recent widely discussed example of the so-called “rare Earth” hypothesis in planetary sciences and astrobiology. The argument is based on the alleged “rarity” of some crucial ingredient for the planetary habitability, which is, in Earth’s case, provided by contingent evolutionary development. For instance, the claim that a contingent fact of history which has created planet Jupiter enables shielding of Earth from most dangerous impact catastrophes, thus increasing Earth’s habitability, leads often to the conclusion that such state-of-affairs must be rare in the Galaxy. I argue that this reasoning is deeply flawed, for several closely related reasons. In addition, the relevance of the philosophical problem of transworld identity for this kind of historical reasoning in science is put forward. This highlights many explanatory problems one faces when using historical counterfactuals in study of complex, nonlinear dynamical systems - and bolsters the relevance of philosophy for evaluation of scientific explanatory claims. [Projekat Ministarstva nauke Republike Srbije, br. ON176021 i br. ON 179048]

Gray (2015) argued that the Fermi paradox (FP) is a misnomer, and it is not a valid paradox. Gray also speculated that the argument was misattributed to Fermi, whose lunchtime remarks did not pertain to the existence of extraterrestrial intelligence, but to the feasibility of interstellar travel. Instead, the paradox is ascribed to Hart and Tipler, and it is further suggested that the paradox is not a real problem or research subject and should not be used in debates about SETI projects. The arguments given are unpersuasive, ahistorical, and, in at least one instance, clearly hinge on literalistic and uncharitable reading of evidence. Instead, I argue the following three points: (i) Contrary to Gray's assertion, the historical issue of naming of ideas or concepts is completely divorced from their epistemic status. (ii) FP is easily and smoothly generalized into the Great Silence paradox, so it makes no sense either theoretically or empirically to separate the two. (iii) In sharp contrast to the main implication of Gray's paper, FP has become more aggravated lately due to advances in astrobiology., Reply to arXiv:1605.09187

In a recent paper in this journal, Ken Olum attempts to refute the doomsday argument by appealing to the self-indication assumption (SIA) that your very existence gives you reason to think that there are many observers. Unlike earlier users of this strategy, Olum tries to counter objections that have been made against (SIA). We argue that his defence of (SIA) is unsuccessful. This does not, however, mean that one has to accept the doomsday argument (or the other counter-intuitive results that flow from related thought-experiments). A developed theory of observation selection efects shows why the doomsday argument is inconclusive, and how one can consistently reect both it and (SIA). I. THE RELATION BETWEEN THE DOOMSDAY ARGUMENT AND (SIA) The doomsday argument purports to show that we have systematically underestimated the probability that humankind will become extinct relatively soon. Originated by Brandon Carter and developed at length by John Leslie,' the doomsday argument argues that we have neglected to take fully into account the indexical information residing in the fact about when in the history of the human species we exist. In a nutshell, your birth rank (i.e., your position in the sequence of all humans) is roughly 70o billion. That you should have such a low birth rank is less surprising, and more probable, if the total number of humans that will ever have existed is, say, 2oo billion rather than, say, 200 trillion. (By 'probability' we here mean rational subjective credence.) Given these unequal conditional probabilities, one can derive from Bayes' theorem that the probability of impending doom goes up after conditionalizing on your birth rank. That is, after realizing the full evidential import

We review the history and status of the famous classification of extraterrestrial civilizations given by the great Russian astrophysicist Nikolai Semenovich Kardashev, roughly half a century after it has been proposed. While Kardashev's classification (or Kardashev's scale) has often been seen as oversimplified, and multiple improvements, refinements, and alternatives to it have been suggested, it is still one of the major tools for serious theoretical investigation of SETI issues. During these 50+ years, several attempts at modifying or reforming the classification have been made; we review some of them here, together with presenting some of the scenarios which present difficulties to the standard version. Recent results in both theoretical and observational SETI studies, especially the G-hat infrared survey (2014-2015), have persuasively shown that the emphasis on detectability inherent in Kardashev's classification obtains new significance and freshness. Several new movements and conceptual frameworks, such as the Dysonian SETI, tally extremely well with these developments. So, the apparent simplicity of the classification is highly deceptive: Kardashev's work offers a wealth of still insufficiently studied methodological and epistemological ramifications and it remains, in both letter and spirit, perhaps the worthiest legacy of the SETI "founding fathers"., Comment: 15 pages, 2 figures, 2 tables

We consider global catastrophic risks due to cosmic explosions (supernovae, magnetars and gamma-ray bursts) and possible mitigation strategies by humans and other hypothetical intelligent beings. While by their very nature these events are so huge to daunt conventional thinking on mitigation and response, we wish to argue that advanced technological civilizations would be able to develop efficient responses in the domain of astroengineering within their home planetary systems. In particular, we suggest that construction of shielding swarms of small objects/particles confined by electromagnetic fields could be one way of mitigating the risk of cosmic explosions and corresponding ionizing radiation surges. Such feats of astroengineering could, in principle, be detectable from afar by advanced Dysonian SETI searches., Comment: Accepted for publication in Acta Astronautica. 21 pages, 1 figure, 1 table

We live in the epoch of explosive development of astrobiology, a novel interdisciplinary field dealing with the origin, evolution and the future of life. The relationship between cosmology and astrobiology is much deeper than it is usually assumed -besides a similarity in the historical model of developmentofthesetwodisciplines, thereisanincreasingnumberofcrossoverproblemsandthematicareas which stem from considerations of Copernicanism and observation selection effects. Such a crossover area is both visualized and heuristically strengthened by introduction of the astrobiological landscape, describing complexity of life in the most general context. We argue that this abstract landscape-like structure in the space of astrobiological parameters is a concept capable of unifying different strands of thought and research, a working concept and not only a metaphor. By analogy with phase spaces of complex physical systems, we can understand the astrobiological landscape as a set of viable evolutionary histories of life in a particular region of space. It is a notion complementary to the classical concept of biological morphological space, underscoring the fact that modern astrobiology offers a prospect of both foundational support and vast extension of the domain of applicability of the Darwinian biological evolution. Such a perspective would strengthen foundations upon which various numerical models can be built; the lack of such quantitative models has often been cited as the chief weakness of the entire astrobiological enterprise. Received 20 May 2012, accepted 11 September 2012, first published online 17 October 2012

We describe a significant practical consequence of taking anthropic biases into account in deriving predictions for rare stochastic catastrophic events. The risks associated with catastrophes such as asteroidal/cometary impacts, supervolcanic episodes, and explosions of supernovae/gamma-ray bursts are based on their observed frequencies. As a result, the frequencies of catastrophes that destroy or are otherwise incompatible with the existence of observers are systematically underestimated. We describe the consequences of this anthropic bias for estimation of catastrophic risks, and suggest some directions for future work.

We review Fermi's paradox (or the "Great Silence" problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi's paradox is certain to tell us something about the future of humanity. Already a more than three quarters of a century old puzzle - and a quarter of century since the last major review paper in the field by G. David Brin - Fermi's paradox has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built into various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypotheses gives, on balance, the strongest justification for guarded optimism regarding our current and near-future SETI efforts., Comment: 39 pages, 3 figures, slightly expanded in comparison to the journal version

Can astrophysics explain Fermi's paradox or the "Great Silence" problem? If available, such explanation would be advantageous over most of those suggested in literature which rely on unverifiable cultural and/or sociological assumptions. We suggest, instead, a general astrobiological paradigm which might offer a physical and empirically testable paradox resolution. Based on the idea of James Annis, we develop a model of an astrobiological phase transition of the Milky Way, based on the concept of the global regulation mechanism(s). The dominant regulation mechanisms, arguably, are gamma-ray bursts, whose properties and cosmological evolution are becoming well-understood. Secular evolution of regulation mechanisms leads to the brief epoch of phase transition: from an essentially dead place, with pockets of low-complexity life restricted to planetary surfaces, it will, on a short (Fermi-Hart) timescale, become filled with high-complexity life. An observation selection effect explains why we are not, in spite of the very small prior probability, to be surprised at being located in that brief phase of disequilibrium. In addition, we show that, although the phase-transition model may explain the "Great Silence", it is not supportive of the "contact pessimist" position. To the contrary, the phase-transition model offers a rational motivation for continuation and extension of our present-day Search for ExtraTerrestrial Intelligence (SETI) endeavours. Some of the unequivocal and testable predictions of our model include the decrease of extinction risk in the history of terrestrial life, the absence of any traces of Galactic societies significantly older than human society, complete lack of any extragalactic intelligent signals or phenomena, and the presence of ubiquitous low-complexity life in the Milky Way.